AMA Manual of Style  Stacy L. Christiansen, Cheryl Iverson 2020
Commonly Used Symbols
Mathematical Composition
Use mathematical symbols in running text only if they are presented with a numerical value within parentheses. These symbols can be used in figures, tables, and boxes with no explanatory footnotes. Some commonly used symbols are as follows:
Symbol 
Description 
> 
greater than 
≥ 
greater than or equal to 
< 
less than 
≤ 
less than or equal to 
± 
plus or minus (This symbol should not be used to indicate variability around a central tendency, eg, “The control group had a mean [SD] value of 12 [7],” not “The control group had a mean of 12 ± 7.”) 
integral from value of a to value of b 

summation from a = 1 to a = 30 

product of a = 1 to a = 30 

Δ 
delta (change, difference between values) 
f 
function 
≠ 
not equal to 
≈ 
approximately equal to 
∼ 
similar to (reserve for use in geometry and calculus, when it can be used in equations to mean “is distributed as”; use words in other cases where “approximately” is meant) 
≅ 
congruent to 
≡ 
defined as 
∴ 
therefore 
∞ 
infinity 
! 
factorial, eg, n! = n(n − 1) (n − 2) . . . 1 
The following symbols are usually reserved for specific values:
π 
pi (approximately 3.1416; do not confuse with uppercase Π) 
e 
base of the system of natural logarithms (approximately 2.7183; see 20.3.3, Logarithmic Expressions; in statistical equations, however, “e” represents the error term in a regression equation) 
i 
the square root of −1 
For a list of additional symbols that are used in statistics, see 19.6, Statistical Symbols and Abbreviations.
The following are examples of these commonly used mathematical expressions:
>10^{5} CFUs/mL
24.5 ± 0.5
L ≈ 2 × 10^{10} m
f (x) = x + Δx
y = dx/dt
P < .001
P < 10 × 3^{—10} (for very small P values, do not use “e” to represent the exponent; see 19.4.2, Rounding)
r ! (n − r)!
(e^{x} + e^{−x})/2
Y = β_{1 }+ β_{2 }+ e
kg ⋅ m ⋅ s^{−2}
(in this case the operation sign is indicated on both sides of the ellipses)
Any symbols rendered in HTML should be compatible across most commonly used browser platforms.